The present invention relates to a method for detecting hydroplaning conditions for vehicle tires as well as a device for performing the inventive method.
Hydroplaning, i.e., the loss of contact of the vehicle tire with the road surface due to formation of a film of water, represents a considerable danger for operating a vehicle. A special danger lies in the fact that hydroplaning occurs without warning signs that are detectable by the driver.
The required friction for transferring braking, acceleration, and lateral guiding forces between the vehicle tire and the road surface is only provided in a sufficient amount when the vehicle tire during rolling on a road surface having a water film thereon is able to displace this water film at least to a substantial portion of the contact surface (the flattened surface of the tire in contact with the road surface during driving, also conventionally referred to as "contact patch" or "contact zone") of the tire so that in this area a direct contact between vehicle tire and road surface is ensured. This displacement of the water film occurs in part due to the drainage properties of the road surface and in part due to the drainage properties of the negative tread portions of the vehicle tire. Since the amount of water that can be displaced by drainage per time unit by the contact of the tire is limited, a so-called water wedge is formed at the leading edge of the contact surface of the tire with increasing vehicle velocity and as a function of the water level. The more the velocity increases, the farther the water wedge is forced under the contact surface of the tire. The horizontal forces which are required for a safe vehicle operation can then be transferred only within the rearward portion of the contact surface of the tire that has not yet been affected by the water wedge.
Upon further insertion of the water wedge between the contact surface of the tire and the road surface, the actual contact area is reduced between the tire and the road surface. In the end, the vehicle tire skids on the hydrodynamic water film. In this state, which is called hydroplaning, horizontal forces can no longer be transmitted. Due to the loss of the lateral guiding forces and of possible braking forces, the vehicle is no longer controllable in this state.
Since the driver becomes aware of the danger of hydroplaning during steering only after the loss of lateral guiding forces, the possibility of a prewarning is practically non-existent. The driver is only able to generally estimate whether the danger of hydroplaning is present due to the presence of a water film on the road surface and as a function of the respective speed of the vehicle.
It is therefore an object of the present invention to provide a method of the aforementioned kind with which the imminent danger of hydroplaning can be detected at an early stage.